[3.9] bpo-37116: Use PEP 570 syntax for positional-only parameters. (GH-12620)

Turn deprecation warnings added in 3.8 into TypeError.
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 8fee1c6..c300270 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -556,11 +556,9 @@
         with self.assertRaises(TypeError):
             class B:
                 method = functools.partialmethod()
-        with self.assertWarns(DeprecationWarning):
+        with self.assertRaises(TypeError):
             class B:
                 method = functools.partialmethod(func=capture, a=1)
-        b = B()
-        self.assertEqual(b.method(2, x=3), ((b, 2), {'a': 1, 'x': 3}))
 
     def test_repr(self):
         self.assertEqual(repr(vars(self.A)['both']),